Geogrid made from a coextruded multilayered polymer

ABSTRACT

An integral geogrid includes a plurality of interconnected, oriented strands having an array of openings therein that is produced from a coextruded multilayer polymer sheet starting material. By virtue of the construction, the coextruded multilayer sheet components provide a crystalline synergistic effect during extrusion and orientation of the integral geogrid, resulting in enhanced material properties that provide performance benefits to use of the integral geogrid in soil geosynthetic reinforcement.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to U.S. ProvisionalApplication for Patent No. 62/239,416 filed Oct. 9, 2015.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to integral geogrids and otheroriented grids used for structural or construction reinforcement andother geotechnical purposes, More particularly, the present inventionrelates to such integral geogrids made from a coextruded multilayerpolymer sheet in order to achieve enhance& stiffness characteristics, aswell as other desirable characteristics as disclosed herein.

This invention also relates to the method of producing such integralgeogrids. Lastly, the present invention relates to the use of suchintegral geogrids for soil and particulate reinforcement and methods ofsuch reinforcement.

For the purpose of this invention, the term “integral geogrid” isintended to include integral geogrids and other integral grid structuresmade by orienting (stretching) a polymeric starting material in the formof a sheet or a sheet-like shape of a requisite thickness and havingholes or depressions made or formed therein.

2. Description of the Prior Art

Polymeric integral grid structures having mesh openings defined byvarious geometric patterns of substantially parallel, orientated strandsand junctions therebetween, such as integral geogrids, have beenmanufactured for over 25 years. Such grids are manufactured by extrudingan integrally cast sheet which is subjected to a defined pattern ofholes or depressions followed by the controlled uniaxial or biaxialstretching and orientation of the sheet into highly oriented strands andpartially oriented junctions defined by mesh openings formed by theholes or depressions. Such stretching and orienting of the sheet ineither uniaxial or biaxial directions develops strand tensile strengthand modulus in the corresponding stretch direction. These integraloriented polymer grid structures can be used for retaining orstabilizing particulate material of any suitable form, such as soil,earth, sand, clay, gravel, etc.

and in any suitable location, such as on the side of a road or othercutting or embankment, beneath a road surface, runway surface, etc.

Various shapes and patterns of holes have been experimented with toachieve higher levels of strength to weight ratio, or to achieve fasterprocessing speeds during the manufacturing process. Orientation isaccomplished under controlled temperatures and strain rates. Some of thevariables in this process include draw ratio, molecular weight,molecular weight distribution, and degree of branching or cross linkingof the polymer.

The manufacture and use of such integral geogrids and other integralgrid structures can be accomplished by well-known techniques. Asdescribed in detail in U.S. Pat. No. 4,374,798 to Mercer, U.S. Pat. No.4,590,029 to Mercer, U.S. Pat. No. 4,743,486 to Mercer and Martin, U.S.Pat. No. 4,756,946 to Mercer, and U.S. Pat. No. 5,419,659 to Mercer, astarting polymeric sheet material is first extruded and then punched toform the requisite defined pattern of holes or depressions. The integralgeogrid is then formed by the requisite stretching and orienting thepunched sheet material

Such integral geogrids, both uniaxial integral geogrids and biaxialintegral geogrids (collectively “integral geogrids,” or separately“uniaxial integral geogrid(s)” or “biaxial integral geogrid(s)”) wereinvented by the aforementioned Mercer in the late 1970 s and have been atremendous commercial success over the past 30 years, totallyrevolutionizing the technology of reinforcing soils, roadwayunderpavements and other civil engineering structures made from granularor particulate materials.

Mercer discovered that by starting with a relatively thick,substantially uniplanar polymer starting sheet, preferably on the orderof 1.5 mm (0.059055 inch) to 4.0 mm (0.15748 inch) thick, having apattern of holes or depressions whose centers lie on a notionalsubstantially square or rectangular grid of rows and columns, andstretching the starting sheet either unilaterally or biaxially so thatthe orientation of the strands extends into the junctions, a totally newsubstantially uniplanar integral geogrid could be formed. As describedby Mercer, “uniplanar” means that all zones of the sheet-like materialare symmetrical about the median plane of the sheet-like material.

In U.S. Pat Nos. 3,252,181, 3,317,951, 3,496,965, 4,470,942, 4,808,358and 5,053,264, the starting material with the requisite pattern of holesor depressions is formed in conjunction with a cylindrical polymerextrusion and substantial uniplanarity is achieved by passing theextrusion over an expanding mandrel. The expanded cylinder is then slitlongitudinally to produce a flat substantially uniplanar starting sheet.

Another integral geogrid is described in U.S. Pat. No. 7,001,112 toWalsh (hereinafter the “Walsh '112 patent”), assigned to Tensarinternational Limited, an associated company of the assignee of theinstant application for patent, Tensar International Corporation, Inc.(hereinafter “Tensar”) of Atlanta, Georgia. The Walsh '112 patentdiscloses oriented polymer integral geogrids including a biaxiallystretched integral geogrid in which oriented strands form triangularmesh openings with a partially oriented junction at each corner, andwith six highly oriented strands meeting at each junction (hereinaftersometimes referred to herein as “triaxial integral geogrid”).

It is intended that the present invention be applicable to all integralgrids regardless of the method of starting sheet formation or of themethod of orienting the starting material into the integral geogrid orgrid structure.

The subject matter of the foregoing U.S. Pat. Nos. 3,252,181, 3,317,951,3,496,965, 4,470,942, 4,808,358, 5,053,264 and 7,001,112 is expresslyincorporated into this specification by reference as if the disclosureswere set forth herein in their entireties. These patents are cited asillustrative, and are not considered to be inclusive, or to excludeother techniques known in the art for the production of integral polymergrid materials.

Traditionally, the polymeric materials used in the production ofintegral geogrids have been high molecular weight homopolymer orcopolymer polypropylene, and high density, high molecular weightpolyethylene. Various additives, such as ultraviolet light inhibitors,carbon black, processing aids, etc., are added to these polymers toachieve desired effects in the finished product and/or manufacturingefficiency.

And, also traditionally, the starting material for production of such anintegral geogrid has typically been a uniplanar sheet that has amonolayer construction, i.e., a homogeneous single layer of a polymericmaterial.

While an integral geogrid produced from the above-described conventionalstarting materials exhibits generally satisfactory properties, it isstructurally and economically advantageous to produce an integralgeogrid having a relatively higher degree of stiffness suitable for thedemands of services such as geosynthetic reinforcement or having otherproperties desirable for particular geosynthetic applications.

Therefore, a need exists for a starting material not only that issuitable for the process constraints associated with the production ofintegral geogrids, but also that once the integral geogrid has beenproduced and is in service, provides a higher degree of stiffness thanthat associated with conventional geogrid starting materials or providesother desirable properties not available with current monolayer integralgeogrids.

SUMMARY OF THE INVENTION

To attain the aforementioned higher degree of stiffness and otherdesirable characteristics, the present invention employs a coextrudedmultilayer polymer sheet as the starting material for the fabrication ofthe integral geogrid.

The experiments described herein support the inventors' theory that byvirtue of the inventive construction, the coextruded multilayer sheetcomponents provide a crystalline synergistic effect during extrusion andorientation, resulting in enhanced material properties that provideperformance benefits to use of the integral geogrid in soil geosyntheticreinforcement.

According to one embodiment of the present invention, a startingmaterial for making an integral geogrid includes a coextruded multilayerpolymer sheet having holes or depressions therein that provide openingswhen the starting material is uniaxially or biaxially stretched.

According to another embodiment of the present invention, an integralgeogrid includes a plurality of highly oriented strands interconnectedby partially oriented junctions and having an array of openings thereinthat is produced from a coextruded multilayer polymer sheet. Accordingto one embodiment of the invention, the integral geogrid is a triaxialintegral geogrid.

According to still another embodiment of the present invention, a soilconstruction includes a mass of particulate material strengthened byembedding therein an integral geogrid produced from a coextrudedmultilayer polymer sheet.

According to yet another embodiment of the present invention, a methodof making a starting material for an integral geogrid includes providinga coextruded multilayer polymer sheet, and providing holes ordepressions therein.

According to another embodiment of the present invention, a method ofmaking an integral geogrid includes providing a coextruded multilayerpolymer sheet, providing holes or depressions therein, and uniaxially orbiaxially stretching the coextruded multilayer polymer sheet having theholes or depressions therein so as to provide a plurality of highlyoriented strands interconnected by partially oriented junctions andhaving an array of the openings therein. According to one embodiment ofthe invention, the method produces a triaxial integral geogrid from acoextruded multilayer polymer sheet.

And, according to yet another embodiment of the present invention, amethod of strengthening a mass of particulate material includesembedding in the mass of particulate material an integral geogridproduced from a coextruded multilayer polymer sheet.

Accordingly, it is an object of the present invention to provide astarting material for making an integral geogrid. The starting materialincludes a coextruded multilayer polymer sheet having holes ordepressions therein that provide openings when the starting material isuniaxially or biaxially stretched.

Another object of the present invention is to provide an integralgeogrid having a plurality of highly oriented strands interconnected bypartially oriented junctions and having an array of openings thereinthat is produced from a coextruded multilayer polymer sheet. Anassociated object of the invention is to provide an integral geogridcharacterized by a higher degree of stiffness, a greater strength, andother desirable characteristics. Specifically, an object of the presentinvention is to provide a triaxial integral geogrid from a coextrudedmultilayer polymer sheet.

Still another object of the present invention is to provide a soilconstruction that includes a mass of particulate material strengthenedby embedding therein an integral geogrid produced from a coextrudedmultilayer polymer sheet.

Yet another object of the present invention is to provide a method ofmaking a starting material for an integral geogrid that includesproviding a coextruded multilayer polymer sheet, and providing holes ordepressions therein.

Another object of the present invention is to provide a method of makingan integral geogrid. The method includes providing a coextrudedmultilayer polymer sheet, providing holes or depressions therein, anduniaxially or biaxially stretching the coextruded multilayer polymersheet having the holes or depressions therein so as to provide aplurality of highly oriented strands interconnected by partiallyoriented junctions and having an array of the openings therein. Themethod can employ known geogrid fabrication methods, such as thosedescribed in the aforementioned U.S. Pat. Nos. 4,374,798, 4,590,029,4,743,486, 5,419,659, and 7,001,112, as well as in other patents.Specifically, an object of the present invention is to provide a methodof making a triaxial integral geogrid from a coextruded multilayerpolymer sheet.

And, still another object of the present invention is to provide amethod of strengthening a mass of particulate material by embedding inthe mass of particulate material an integral geogrid produced from acoextruded multilayer polymer sheet.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described, reference being had tothe accompanying drawings forming a part hereof, wherein like referencenumbers refer to like parts throughout. The accompanying drawings areintended to illustrate the invention, but are not necessarily to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a coextruded uniplanar multilayer sheet startingmaterial for an integral geogrid, before holes or depressions are formedtherein according to one embodiment of the present invention.

FIG. 2 is a perspective plan view of the starting material sheet shownin FIG. 1 that has the holes punched therein for forming a triaxialintegral geogrid of the type shown in the Walsh '112 patent.

FIG. 3 is a side view of a section of the starting material sheet shownin FIG. 2.

FIG. 4 is a plan view of a section of the triaxial integral geogridproduced by biaxially orienting the starting material sheet shown inFIG. 2.

FIG. 5 is a perspective view of the section of the triaxial integralgeogrid shown in FIG. 4.

FIG. 6 is an enlarged perspective view of the section of the triaxialintegral geogrid shown in FIG. 4.

FIG. 7 is a side cross-sectional view of the section of the triaxialintegral geogrid shown in FIG. 4.

FIG. 8 is a table summarizing aperture stability modulus properties foran experimental triaxial integral geogrid produced from a 3 mmcoextruded uniplanar multilayer sheet starting material such as shown inFIGS. 1-7 to be compared with similar properties of a triaxial integralgeogrid commercially available from Tensar as a TriAx® TX140™ geogrid.

FIG. 9 is a table comparing various product properties of triaxialintegral geogrids commercially available from Tensar (produced fromextruded monolayer sheets) with corresponding various product propertiesof experimental triaxial integral geogrids as shown in FIGS. 4-7produced from coextruded uniplanar multilayer sheets according to thepresent invention.

FIG. 10 is another table comparing various product properties oftriaxial integral geogrids commercially available from Tensar (producedfrom extruded monolayer sheets) with corresponding product properties ofexperimental triaxial integral geogrids produced from coextrudeduniplanar multilayer sheets according to the present invention.

FIG. 11 is a perspective view of a section of a triaxial integralgeogrid according to another embodiment of the present invention.

FIG. 12 is a plan view of the section of the triaxial integral geogridshown in FIG. 11.

FIG. 13 is a side cross-sectional view of the section of the triaxialintegral geogrid shown in FIG. 11.

FIG. 14 illustrates a coextruded uniplanar multilayer sheet startingmaterial for an integral geogrid, before holes or depressions are formedtherein according to another embodiment of the present invention.

FIG. 15 is a perspective view of a section of a triaxial integralgeogrid associated with the starting material sheet shown in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although only preferred embodiments of the invention are explained indetail, it is to be understood that the invention is not limited in itsscope to the details of construction and arrangement of components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced orcarried out in various ways.

Also, in describing the preferred embodiments, terminology will beresorted to for the sake of clarity. It is intended that each termcontemplates its broadest meaning as understood by those skilled in theart, and includes all technical equivalents which operate in a similarmanner to accomplish a similar purpose.

And, as used herein, the terms “coextruded,” “coextruding,” and“coextrusion” are used according to their commonly accepted definition,i.e., pertaining to a single-step process starting with two or morepolymeric materials that are simultaneously extruded and shaped in asingle die to form a multilayer sheet.

The present invention is directed to uniaxial, biaxial, and triaxialintegral geogrid structures produced from a coextruded multilayerpolymer sheet as the starting material. The coextruded multilayerpolymer sheet starting material can be, for example, uniplanar, or canbe non-uniplanar, depending upon the particular characteristics that aredesired for the multilayer geogrid structure that is to be fabricatedtherefrom. According to a preferred embodiment of the invention, thecoextruded multilayer polymer sheet starting material is uniplanar orsubstantially uniplanar.

The invention is based on the fact that extrusion of the coextrudedmultilayer sheet consisting of different polymeric materials or otherextrudable materials at varying percentage content when converted touniaxial, biaxial, and/or triaxial integral geogrids via a sheetpunching and oven stretching process, produces a finished product thathas unique characteristics relative to the traditional uniaxial,biaxial, and triaxial geogrids for purposes of soil reinforcement andother geotechnical applications.

FIG. 1 illustrates a coextruded multilayer sheet 100 used as a startingmaterial for an integral geogrid according to one embodiment of thepresent invention, before the sheet has been through-punched ordepressions formed therein.

As shown in FIG. 1, the coextruded multilayer sheet 100 is a three-layersheet embodiment of the invention. That is, preferably, sheet 100includes a first layer 110, a second layer 120, and a third layer 130.The first layer 110 and the third layer 130 are arranged on oppositeplanar surfaces of second layer 120, preferably in a uniplanar orsubstantially uniplanar configuration. Further, while the three-layerconfiguration of sheet 100 is shown for purposes of illustration, theinvention contemplates the use of a sheet having multiple layersarranged in various configurations, multiple layers having variouscombinations of thicknesses, and multiple layers having variousmaterials of construction, all as dictated by the particular applicationin which the integral geogrid is to be employed. For example, while thethree-layer configuration of sheet 100 is shown for purposes ofillustration, the invention also contemplates the use of coextrudedsheets having more than three layers. In general, the layerconfiguration, the layer thicknesses, and the materials of constructionof the layers are selected to provide not only ease of fabrication ofthe integral geogrid, but also an integral geogrid having the desireddegree of stiffness and other performance properties.

As described above, the coextruded multilayer sheet 100 used as thestarting material for an integral geogrid according to the presentinvention is preferably through-punched, although it may be possible touse depressions formed therein instead. According to the embodiment ofthe starting material in which depressions are formed in the sheet, thedepressions are provided on each side of the sheet, i.e., on both thetop and the bottom of the sheet. Further, the depressions extend intoeach layer of the coextruded multilayer sheet.

In the particular embodiment of the invention shown in FIG. 1, the sheet100 is made by coextruding a first material that forms the first layer110, a second material that forms the second layer 120, and a thirdmaterial that forms the third layer 130 in a manner known to thoseskilled in the art of extruding multi-layer sheets.

According to a preferred embodiment of the invention, the overallthickness of the sheet 100 is from about 2 mm to about 12 mm and,according to a more preferred embodiment of the invention, the overallthickness of the sheet 100 is from about 2 mm to about 6 mm.

With regard to the individual thicknesses of the sheet layers, accordingto a preferred embodiment of the invention, the thickness of the firstlayer 110 is from about 0.5 mm to about 4.5 mm, the thickness of thesecond layer 120 is from about 1 mm to about 9 mm, and the thickness ofthe third layer 130 is from about 0.5 mm to about 4.5 mm, keeping inmind that the overall thickness of the sheet 100 is from about 2 mm toabout 12 mm. And, according to a more preferred embodiment of theinvention, the thickness of the first layer 110 is from about 0.5 mm toabout 2 mm, the thickness of the second layer 120 is from about 2 mm toabout 5 mm, and the thickness of the third layer 130 is from about 0.5mm to about 2 mm.

In general, the material of construction of the first layer 110, thesecond layer 120, and the third layer 130 may be the same as each other,or may be different from one another. Preferably, the material ofconstruction of the first layer 110 and the material of construction ofthe third layer 130 may be the same as each other, or may be differentfrom one another. More preferably, material of construction of thesecond layer 120 is different from the material of construction of boththe first layer 110 and the material of construction of the third layer130.

And, in general, the layers of the sheet are polymeric in nature. Forexample, the materials of construction may include high molecular weightpolyolefins, and broad specification polymers. Further, the polymericmaterials may be virgin stock, or may be recycled materials, such as,for example, post-industrial or post-consumer recycled polymericmaterials. And, the use of one or more polymeric layers having a lowercost than that of the aforementioned high molecular weight polyolefinsand broad specification polymers is also contemplated. The use of such alower cost polymeric layer may result in a cost savings of approximately20% to approximately 30% relative to the use of, for example, apolypropylene layer.

According to a preferred embodiment of the invention, the material ofconstruction of the first layer 110 and the third layer 130 is a highmolecular weight polyolefin, such as, for example, a polypropylene(“PP”). And, according to the same preferred embodiment, the material ofconstruction of the second layer 120 is a broad specification polymer,such as, for example, a virgin PP, or a recycled PP, such as, forexample, a post-industrial PP or other recycled PP. However, dependingupon the particular application of the integral geogrid, polymericcomponents having a material of construction other than polypropylenemay be included in the coextruded multilayer sheet.

FIGS. 2 and 3 illustrate the coextruded multilayer sheet startingmaterial 100 of FIG. 1 that has holes 140 punched therein for formingthe triaxial integral geogrid 200 shown in FIGS. 4, 5, and 6. The sizeand spacing of the holes 140 are as disclosed in the Walsh '112 patent.The triaxial integral geogrid 200 includes highly oriented strands 205and partially oriented junctions 235, also as disclosed in the Walsh'112 patent. The upper layer 130 of the starting material 100 has beenstretched and oriented into the upper layer 230 of the strands 205 andjunctions 235. Similarly, the third or lower layer 110 of the startingmaterial 100 has been stretched and oriented into the lower orunderneath layer 210 of the strands 205 and junctions 235. As the firstlayer 130 and third layer 110 are being stretched and oriented, thesecond or middle layer 120 is also being stretched and oriented intomiddle layer 220 of both the strands 205 and junctions 235.

The invention also relates to a method of making the above-describedtriaxial integral geogrid 200. The method includes: providing thecoextruded multilayer polymer sheet 100; forming a plurality of holes ordepressions in the coextruded multilayer polymer sheet 100 in a selectedpattern, such as in accordance with the disclosure of the Walsh '112patent; and biaxially stretching and orienting the coextruded multilayerpolymer sheet having the patterned plurality of holes or depressionstherein to form an integral geogrid having a plurality ofinterconnected, oriented strands between partially oriented junctionsand to configure the holes or depressions as grid openings.

In general, once the coextruded multilayer polymer sheet 100 has beenprepared with holes or depressions, the triaxial integral geogrid 200can be produced from the sheet 100 according to the methods described inthe above-identified patents and known to those skilled in the art.

To demonstrate the enhanced characteristics and properties of theinventive integral geogrid produced from the coextruded multilayersheet, comparative tests were performed.

FIG. 8 is a table summarizing aperture stability modulus properties foran experimental triaxial integral geogrid produced from a 3 mmcoextruded sheet starting material to be compared with similarproperties of a triaxial integral geogrid commercially available fromTensar as a TriAx® TX140™ geogrid. The experiment was performedaccording to the testing protocols of ASTM D7864, i.e., the “StandardTest Method for Determining the Aperture Stability Modulus of Geogrid.”The aperture stability testing was performed on triaxial integralgeogrid samples made from a 3 mm thick coexruded multilayer sheet thatincluded 50% BSR (“broad specification resin”) that had been punched.and stretched. The first i.e., lower, layer 110 of the coextrudedmultilayer sheet had a material of construction of a high molecularweight polypropylene (PP) and a thickness of 0.75 mm; the second, i.e.,middle, layer 120 had a material of construction of a broadspecification PP and a thickness of 1.50 mm; and the third, i.e., upper,layer 130 had a material of construction of a high molecular weight PPand a thickness of 0.75 mm.

For the experimental laboratory-prepared triaxial integral geogrid madefrom the coextruded multilayer sheet, the average value for a moment of20 cm-kg was 70 cm-kg/deg. Conversely, for the non-coextruded, i.e.,monolayer sheet, specifically from six tests of the standard Triax®TX140™ geogrids, the average value of the tests was 2.86 cm-kg/deg, witha range of 2.52 to 3.14 cm-kg/deg, substantially below the average valuerecorded for the experimental multilayer samples.

FIG. 9 also illustrates various product properties of triaxial integralgeogrids produced from monolayer extruded sheets with correspondingproduct properties of triaxial integral geogrids produced fromcoextruded multilayer sheets according to the present invention. In thetests summarized in FIG. 9, the monolayer sheets were processed to havethe configuration of the triaxial integral geogrid described in theWalsh '112 patent. Such a triaxial integral geogrid is commerciallyavailable from Tensar, and is known as the TriAx® TX160™ geogrid.

For the comparative experiments shown in FIG. 9, coextruded 3-layersheets in 4.6 mm finished sheet thicknesses were prepared. The varioussheets incorporated different loadings of post-industrial polypropylene(PP) content, and each of the coextruded 3-layer sheets was thenprocessed into a triaxial integral geogrid comparable to Tensar's TriAx®TX160™ geogrid.

With regard to FIG. 9, each of the 4.6 mm coextruded multilayer sheetsincluded the following layer compositions: Sample (1) a first or upperlayer 130, as described above, of 34% virgin polypropylene (PP) andblack masterbatch (“MB,” i.e., black carbon to provide a black color tothe product for UV protection)/a second or middle layer 120, asdescribed above, of 32% post-industrial PP/and a third or lower layer110, as described above, of 34% virgin PP and MB; and Sample (2) 25%virgin PP and MB/50% post-industrial PP/25% virgin PP and MB.

The thickness of each of the above-described layers for the varioussheet Samples (1) and (2) is as follows. For the 4.6 mm multilayer sheetSample (1), the thicknesses of the layers were, respectively: 1.56mm/1.47 mm/1.56 mm. For the 4.6 mm multilayer sheet Sample (2), thethicknesses of the layers were, respectively: 1.15 mm/2.30 mm/1.15 mm.

As is evident from the results presented in FIG. 9, the resultantexperimental triaxial integral geogrids produced from theabove-described punched and oriented 4.6 mm coextruded 3-layer sheetsamples resulted in a product, versus the standard monolayered Triax®TX160™ geogrid with the approximate equivalent starting sheet thickness(4.7 mm), that exhibited substantially higher product stiffness asmeasured per standard Tensar low strain tensile modulus testing,flexural stiffness testing, and aperture stability testing. The 0.5% and2.0% strain tensile modulus test values were more than 30% stronger forthe experimental triaxial geogrids produced from the 4.6 mm coextruded3-layer starting sheet than from the conventional Triax® TX160™ geogridsproduced from the 4.7 mm monolayered sheet. Similarly, the flexuralstiffness measured more than 33% higher for the experimental triaxialgeogrids produced from the 4.6 mm coextruded sheet than the standardTriax® TX160™ geogrid made from a 4.7 mm monolayered starting sheet.

FIG. 10 is another table comparing various product properties oftriaxial integral geogrids produced from monolayer sheets commerciallyavailable from Tensar with corresponding product properties ofexperimental triaxial integral geogrids produced from coextrudedmultilayer sheets according to the present invention. In the testssummarized in FIG. 10, the monolayer sheets were also processed to havethe configuration of the triaxial integral geogrid described in theWalsh '112 patent. Such a triaxial integral geogrid is commerciallyavailable from Tensar, and is known as the TriAx® TX140™ geogrid.

For the comparative experiments shown in FIG. 10, coextruded 3-layersheets in 3.0 mm finished sheet thicknesses were prepared. The varioussheets incorporated different loadings of post-industrial polypropylene(PP) content, and each of the coextruded 3-layer sheets was thenprocessed into a triaxial integral geogrid comparable to Tensar's TriAx®TX140™ geogrid.

With regard to FIG. 10, Sheet “SN20140407” had the followingcomposition: 32% broad specification resin in the second (i.e., middle)layer 120 and 34% high molecular weight PP in the first (i.e. top) layer130 and in the third (i.e., lower) layer 110. Sheet “SN20140408” had thefollowing composition: 50% broad specification resin in the second(i.e., middle) layer, and 25% high molecular weight PP in the firstlayer and in the third layer. Sheet “SN20140409” had the followingcomposition: 60% broad specification resin in the second (i.e., middle)layer, and 20% high molecular weight PP in the first layer and in thethird layer.

The thickness of each of the above-described layers for SheetSN20140407, Sheet SN20140408, and Sheet SN20140409 is as follows. Forthe 3 mm multilayer Sheet SN20140407, the thicknesses of the first, thesecond, and the third layers were, respectively: 1.02 mm/0.96 mm/1.02mm. For the 3 mm multilayer Sheet SN20140408, the thicknesses of thelayers were, respectively: 0.75 mm/1.5 mm/0.75 mm. For the 3 mmmultilayer Sheet SN20140409, the thicknesses of the layers were,respectively: 0.6 mm/1.8 mm/0.6 mm.

As is evident from the results reported in FIG. 10, the 3.0 mm startingsheet thickness with post-industrial PP content of 32% (SN20140407), 50%(SN20140408), and 60% (SN20140409), when converted to a finishedtriaxial integral geogrid, exceeded the only specified tensile modulustest for Triax® TX140™ geogrid produced from a 3.7 mm thick sheet whichis 220 kN/m in the transverse direction (“TD”). FIG. 10 also shows thateach of the coextruded samples, starting with the thinner 3.0 mm sheet,met or exceeded the average tensile modulus values of standard Triax®TX140™ geogrid produced from a 3.7 mm sheet.

Again, the experiments described herein support the inventors' conceptthat by virtue of utilizing a multi-layer construction for the startingmaterial sheet, the coextruded multilayer sheet components can provide acrystalline synergistic effect during extrusion and orientation, thusproviding enhanced material properties in the resultant integral geogridand performance benefits when using the resultant integral geogrid insoil and other geotechnical applications.

Other possible embodiments of the instant invention can include, forexample, (1) multilayer coextruded polymer sheet starting materialshaving significantly higher levels of post-industrial and post-consumerPP resins, i.e., PP resins that have a relatively low cost, (2) foamingagents to provide a foamed or expanded second (i.e., middle) layer, (3)one or more relatively low cost layers that include bulking agents orfillers, (4) a color identification layer within the integral geogrid,and (5) a 3-layer coextruded polymer sheet with HDPE outer layers and anamorphous and crystalline polyester inner layer sandwiched therebetween.Each of the above examples would provide an enhancement or satisfy aneed for an integral geogrid having enhanced geosynthetic aggregatereinforcement, cost reduction and/or identification properties.

More specifically, as indicated above, one possible embodiment of theinstant invention could include the use of a foaming agent to provide afoamed or expanded second or middle layer. FIGS. 11, 12, and 13 aredirected to such an embodiment 300, in which the second or middle layer(here designated as 320) of the coextruded multilayer sheet forms anexpanded or “foamed” structure That is, according to this embodiment ofthe invention, a chemical foaming agent is mixed with the polymer thatis extruded to form the second layer. The heat that is generated to meltthe polymer decomposes the chemical foaming agent, which results in theliberation of a gas. The gas is then dispersed in the polymer melt, andexpands upon exiting the die. As a result, the second layer is expandedor foamed (see FIG. 13, which is a side cross-sectional view of thesection of the integral triaxial geogrid shown in FIG. 11.)

According to this embodiment of the invention, as with theabove-described first embodiment, the material of construction of thefirst layer (here, 310) and the material of construction of the thirdlayer (here, 330) may be the same as each other, or may be differentfrom one another, although the same material is preferred. In general,the material of construction of the second layer 320 is different fromthe material of construction of both the first layer 310 and thematerial of construction of the third layer 330.

Advantages of the foamed embodiment of the finished integral geogridaccording to the present invention not only include reduced raw materialcost and reduced geogrid weight, but also may include desirable physicaland chemical properties of the foamed layer per se.

As indicated above, one possible embodiment of the instant inventioncould include the use of a color identification layer with the integralgeogrid. For example, the American Association of State Highway andTransportation Officials (“AASHTO”) requires, in conjunction with theNational Transportation Product Evaluation Program (“NTPEP”), a productmarker for geosynthetic reinforcements associated with walls, slopes,and fills over soft ground.

The above-described color identification layer could be, for example, apolymeric layer having a color that differs from the color of anadjacent, or an associated, co-extruded layer. The color identificationlayer could be an inner layer or an outer layer of the integral geogrid,or the integral geogrid could include multiple color identificationlayers of either the same color or a variety of colors. The coloridentification layer could be a solid color, or could have a pattern,such as incorporating a stripe. The color and/or chemistry of the coloridentification layer is selected, of course, based upon the requirementsof a particular application of the integral geogrid.

In addition to the above-described use of the integral geogrid's coloridentification layer for compliance with AASHTO and NTPEP standards, thecolor identification layer can also serve to provide sourceidentification of the integral geogrid.

As indicated above, while the three-layer configuration of sheet 100 hasbeen shown for purposes of illustration, the invention also contemplatesthe use of coextruded sheets having more than three layers. For example,the coextruded sheet can be a five-layer configuration, such as sheet400 shown in FIG. 14. Sheet 400 includes a middle layer 420, a firstinner layer 410, a second inner layer 430, a first outer layer 440, anda second outer layer 450. The first inner layer 410 and the second innerlayer 430 are arranged on opposite planar surfaces of middle layer 420,preferably in a uniplanar or substantially uniplanar configuration. Thefirst outer layer 440 and the second outer layer 450 are arranged onopposite planar surfaces of, respectively, first inner layer 410 andsecond inner layer 430, preferably in a uniplanar or substantiallyuniplanar configuration.

In the particular embodiment of the invention shown in FIG. 14, thesheet 400 is made by coextruding a first material that forms the middlelayer 420, a second material that forms the first inner layer 410, athird material that forms the second inner layer 430, a fourth materialthat forms the first outer layer 440, and a fifth material that formsthe second outer layer 450, in a manner known to the those skilled inthe art of extruding multi-layer sheets.

In general, the material of construction of the middle layer 420, thefirst inner layer 410, the second inner layer 430, the first outer layer440, and the second outer layer 450 may be the same as each other, ormay be different from one another. For example, the middle layer 420 mayhave a first material of construction, the first inner layer 410 and thesecond inner layer 430 may have a second material of construction, andthe first outer layer 440 and the second outer layer 450 may have athird material of construction. In summary, depending upon theparticular service application in which the integral geogrid made fromthe sheet 400 is to be employed, various combinations of materials ofconstruction for the above-described five layers may be used.

FIG. 15 is a perspective view of a section of a triaxial integralgeogrid 500 associated with the starting material sheet 400 shown inFIG. 14. The triaxial integral geogrid 500 includes highly orientedstrands 505 and partially oriented junctions 535. After holes have beenpunched in sheet 400, the first outer layer 440 and the second outerlayer 450 of sheet 400 have been stretched and oriented into,respectively, the first outer layer 540 and the second outer layer 550of the strands 505 and junctions 535. Similarly, the first inner layer410 and the second inner layer 430 of sheet 400 have been stretched andoriented into, respectively, the first inner layer 510 and the secondinner layer 530 of the strands 505 and junctions 535. And, as the firstouter layer 440 and the second outer layer 450, and the first innerlayer 410 and the second inner layer 430 are being stretched andoriented, the middle layer 420 is also being stretched and oriented intomiddle layer 520 of both the strands 505 and junctions 535.

As also indicated above, one possible embodiment of the instantinvention could include the use of one or more relatively low costlayers that include bulking agents or fillers. The inclusion of suchbulking agents or fillers in the layers of the integral geogrid create aproduct having a thicker, i.e., loftier, profile, which can lead toenhanced performance of the integral geogrid in certain serviceapplications. Depending upon the service application in which theintegral geogrid is to be employed, such bulking agents or fillers, mayinclude, for example, one or more of CaCO₃ (calcium carbonate), talc,CaSiO₃ (wollastonite), nano-fillers, multi-wall carbon nanotube(“MWCNT”), single wall carbon nanotube (“SWCNT”), glass fibers, andaluminum hydrate.

As described earlier above, the use of one or more polymeric layershaving a lower cost than that of high molecular weight polyolefins andbroad specification polymers is contemplated. In an embodiment in whichsuch a lower cost polymeric layer also includes the aforementionedbulking agent or filler, a cost savings of approximately 20% relative tothe use of, for example, a polypropylene layer, may result.

And, of course, use of the above-described foam layer can also create aproduct having a thicker, i.e., loftier, profile, which can also lead toenhanced performance of the integral geogrid in certain serviceapplications. Contemplated embodiments of the invention include those inwhich one or more of the foamed layers are used in conjunction with oneor more layers that include the bulking agents or fillers.

In general, the instant invention is based on employing the coextrusiontechniques and materials described herein to modify and enhance certainphysical, chemical, and/or mechanical properties of an integral geogridso as to improve the performance of the integral geogrid in a particularapplication thereof.

The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous modifications and changes mayreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation described andshown.

1.-28. (canceled)
 29. An integral geogrid comprising a plurality ofinterconnected, oriented strands having an array of openings therein,the integral geogrid being produced from a multilayer polymer startingsheet having layers of different materials and formed in a singlecoextrusion.
 30. The integral geogrid according to claim 29, wherein theoriented strands have been uniaxially or biaxially stretched.
 31. Theintegral geogrid according to claim 29, wherein the coextrudedmultilayer polymer starting sheet includes a first layer, a secondlayer, and a third layer, with the first layer and the third layer beingarranged on opposite planar surfaces of the second layer.
 32. Theintegral geogrid according to claim 29, wherein the coextrudedmultilayer polymer starting sheet has a thickness of from about 2 mm toabout 12 mm.
 33. The integral geogrid according to claim 31, wherein thefirst layer has a thickness of from about 0.5 mm to about 4.5 mm, thesecond layer has a thickness of from about 1 mm to about 9 mm, and thethird layer has a thickness of from about 0.5 mm to about 4.5 mm. 34.The integral geogrid according to claim 31, wherein the first layer hasa material of construction of a high molecular weight polyolefin, thesecond layer has a material of construction of a broad specificationpolymer, and the third layer has a material of construction of a highmolecular weight polyolefin.
 35. The integral geogrid according to claim34, wherein the high molecular weight polyolefin of the first layer is apolypropylene, the broad specification polymer of the second layer is apost-industrial polypropylene, and the high molecular weight polyolefinof the third layer is a polypropylene.
 36. The integral geogridaccording to claim 29, wherein the plurality of interconnected, orientedstrands includes transverse strands interconnected by substantiallylongitudinally oriented strands.
 37. The integral geogrid according toclaim 29, wherein the integral geogrid is configured for structural orconstruction reinforcement purposes.
 38. A starting material for makingan integral geogrid comprising a multilayer polymer starting sheethaving layers of different materials and formed in a single coextrusion,and having holes or depressions therein that provide openings when thestarting sheet is uniaxially or biaxially stretched.
 39. The startingmaterial according to claim 38, wherein the coextruded multilayerpolymer starting sheet includes a first layer, a second layer, and athird layer, with the first layer and the third layer being arranged onopposite planar surfaces of the second layer.
 40. The starting materialaccording to claim 38, wherein the coextruded multilayer polymerstarting sheet has an initial thickness of at least 2 mm.
 41. Thestarting material according to claim 38, wherein the coextrudedmultilayer polymer starting sheet has a stretched thickness of fromabout 0.2 mm to about 9 mm.
 42. The starting material according to claim38, wherein the coextruded multilayer polymer starting sheet oncestretched exhibits an increased flexural stiffness and torsionalrigidity relative to the flexural stiffness and torsional rigidity of anon-coextruded sheet having a substantially same starting thickness. 43.A soil construction comprising a mass of particulate materialstrengthened by embedding therein an integral geogrid as claimed inclaim
 29. 44. A method of strengthening a mass of particulate material,comprising embedding in the mass of particulate material the integralgeogrid as claimed in claim
 29. 45. A method of making an integralgeogrid, comprising: providing a multilayer polymer starting sheethaving layers of different materials and formed in a single coextrusion;providing a patterned plurality of holes or depressions in thecoextruded multilayer polymer starting sheet; and orienting thecoextruded multilayer polymer starting sheet having the patternedplurality of holes or depressions therein to provide a plurality ofinterconnected, oriented strands and to configure the holes ordepressions as grid openings.
 46. The method according to claim 45,wherein the coextruded multilayer polymer starting sheet having thepatterned plurality of holes or depressions therein is oriented byuniaxial or biaxial stretching.
 47. The method according to claim 45,wherein the coextruded multilayer polymer starting sheet includes afirst layer, a second layer, and a third layer, with the first layer andthe third layer being arranged on opposite planar surfaces of the secondlayer.
 48. The method according to claim 45, wherein the coextrudedmultilayer polymer starting sheet has an initial thickness of at least 2mm.
 49. The method according to claim 45, wherein the first layer has athickness of from about 0.5 mm to about 4.5 mm, the second layer has athickness of from about 1 mm to about 9 mm, and the third layer has athickness of from about 0.5 mm to about 4.5 mm.
 50. The method accordingto claim 45, wherein the first layer has a material of construction of ahigh molecular weight polyolefin, the second layer has a material ofconstruction of a broad specification polymer, and the third layer has amaterial of construction of a high molecular weight polyolefin.
 51. Amethod of providing an integral geogrid construction, comprising:uniaxially or biaxially stretching a starting material that is amultilayer polymer starting sheet having layers of different materialsand formed in a single coextrusion, and having a patterned plurality ofholes or depressions therein, to provide an integral geogrid having aplurality of oriented strands and a plurality of grid openings; andembedding the integral geogrid in a mass of particulate material. 52.The integral geogrid according to claim 29, wherein the integral geogridis a triaxial integral geogrid.
 53. The method according to claim 45,wherein the integral geogrid is a triaxial integral geogrid.
 54. Themethod according to claim 45, wherein the integral geogrid is a uniaxialintegral geogrid.
 55. The method according to claim 45, wherein theintegral geogrid is a biaxial integral geogrid.
 56. The method accordingto claim 45, wherein the integral geogrid includes a coloridentification layer.